1. Field of the Invention
This invention relates to a vacuum heat-treatment apparatus for heat-treating a metal workpiece under vacuum and more particularly to such an vacuum heat-treatment apparatus provided with a workpiece transfer mechanism for transferring a workpiece from a treating cell in the vacuum heat-treatment apparatus to another.
2. Description of the Related Art
As a vacuum heat-treatment apparatus, there has been known a modular vacuum heat-treatment apparatus disclosed in U.S. Pat. No. 6,065,964. The vacuum heat-treatment apparatus comprises a plurality of treating cells horizontally joined to a hermetic chamber having a horizontal shaft. An additional module in the form of a cylinder having therein an additional treating cell can be joined to one end of the hermetic chamber, whereby a desired number of treating cells can be added in a horizontal direction.
Further, there has been disclosed another vacuum heat-treatment apparatus in U.S. Pat. No. 5,033,927. In the vacuum heat-treatment apparatus, a plurality of heating chambers (treating cells) are disposed in a star-like pattern in the upper portion of a doughnut-shaped hermetic chamber and a conveyor carriage which runs along a guide rail to transfer a workpiece from one treating cell to another is provided. The conveyor carriage runs below the treating cells and transfers the workpiece to a desired treating cell.
The vacuum heat-treatment apparatus of the former prior art is disadvantageous in that as the number of the treating cells increases, the overall length of the vacuum heat-treatment apparatus horizontally increases and the time required to transfer the workpiece from a certain treating cell to another certain treating cell is elongated. Depending on the kind of the treatment, the workpiece must be transferred from one cell to another in a short time. Especially in a vacuum heat-treatment apparatus, a metal workpiece heated to a high temperature must be quickly introduced into a hardening oil reservoir or a gas cooling cell in an oil hardening step or a gas cooling step. If it takes a long time to transfer the workpiece from the heating cell to the hardening oil reservoir or the gas cooling cell, the temperature of the workpiece lowers before the workpieces is introduced into the hardening oil reservoir or the gas cooling cell, which deteriorates the quality of the product obtained. Further since the vacuum heat-treatment apparatus is horizontally extended as the number of the treating cells increases, the space occupied by the vacuum heat-treatment apparatus increases in proportion to the number of the treating cells.
The vacuum heat-treatment apparatus of the latter prior art is disadvantageous in that the number of the treating cells is limited by the size of the hermetic chamber and increase of the throughput is limited.
In view of the foregoing observations and description, the primary object of the present invention is to provide a vacuum heat-treatment apparatus which allows a workpiece to be transferred from one of a plurality of treating cells to another treating cell in a short time.
Another object of the present invention is to provide a vacuum heat-treatment apparatus which allows to increase the number of the treating cells without increasing the area occupied by the vacuum heat-treatment apparatus.
In accordance with the present invention, there is provided a vacuum heat-treatment apparatus for heat-treating a workpiece in a treating cell comprising a hermetic chamber disposed at the center, a plurality of treating cells disposed along the periphery of the hermetic chamber, and a workpiece transfer mechanism which is disposed inside the hermetic chamber and transfers the workpiece from one of the treating cells to the hermetic chamber and from the hermetic chamber to one of the treating cells.
The hermetic chamber and/or the treating cells may be provided in two or more stages in a vertical direction.
The workpiece transfer mechanism may comprise, for instance, a workpiece container in which the workpiece is contained, a rotating mechanism which changes the horizontal direction of the workpiece container, and an elevator mechanism which moves up and down the workpiece container.
One of the treating cells may be an oil hardening cell and the oil hardening cell may be disposed in a lower portion of the hermetic chamber.
The workpiece container may be provided with a telescopic lateral movement mechanism on which a basket containing therein the workpiece can be placed. Further, an oil hardening cell disposed along the periphery of the hermetic chamber may be employed as a workpiece input/output cell for taking the workpiece in the vacuum heat-treatment apparatus and discharging the treated workpiece therefrom.
One of the treating cells may be a gas cooling cell and the gas cooling cell may be employed as a workpiece input/output cell for taking the workpiece in the vacuum heat-treatment apparatus and discharging the treated workpiece therefrom.
When the treating cells are provided in two or more stages, it is preferred that the upper and lower treating cells be angularly shifted with respect to each other by half a pitch, i.e., half of the angle included between adjacent two treating cells in the same stage, in order to reserve a space for accommodating a motor for a cooling fan or the like projecting from the top of the treating cell.
In the vacuum heat-treatment apparatus of the present invention, since all the treating cells are disposed along the periphery of the hermetic chamber adjacent to the hermetic chamber, the workpiece can be transferred from one treating cell to another in a short time by way of the hermetic chamber and accordingly a later treatment of a series of vacuum heat treatments can be started within a desired time, whereby a high quality product can be obtained.
Further, the number of the treating cells can be increased according to the required throughput without increasing the area occupied by the vacuum heat-treatment apparatus by increasing the number of the treating cells disposed along the periphery of the hermetic chamber or by providing the hermetic chamber and/or the treating cells in two or more stages in a vertical direction. That is, since the vacuum heat-treatment apparatus of the present invention allows to three-dimensionally increase the treating cells, the throughput can be increased in a limited area.
When the workpiece transfer mechanism comprises a workpiece container in which the workpiece is contained, a rotating mechanism which changes the horizontal direction of the workpiece container and an elevator mechanism which moves up and down the workpiece container, the workpiece can be transferred from one of the treating cells to another by a minimum movement of the workpiece transfer mechanism and accordingly, the workpiece can be freely transferred to a desired treating cell in a short time.
When one of the treating cells is an oil hardening cell, the workpiece can be hardened in a short time by a minimum movement of the workpiece transfer mechanism. Further when the oil hardening cell is disposed in a lower portion of the hermetic chamber, the workpiece can be introduced into the oil hardening cell in substantially the same short time from any one of the treating cells in the same stage to be hardened, and accordingly, high quality products can be constantly obtained.